Things work a little different for Facebook than they do for sites with more reasonable traffic. I've seen a few talks on YouTube where they speak about the challenges of scalability as they gradually hot swap legacy X or Y for their own in-house component Z.
See React/JSX and Flux, and the Haxl library. They go into detail about some of the problems and solutions that they've made public with respect to those projects, and they speak a lot about testing too in many of the posts. Worth checking out.
Things work a little different for Facebook than they do for sites with more reasonable traffic. I've seen a few talks on YouTube where they speak about the challenges of scalability as they gradually hot swap legacy X or Y for their own in-house component Z.
See React/JSX and Flux, and the Haxl library. They go into detail about some of the problems and solutions that they've made public with respect to those projects, and they speak a lot about testing too in many of the posts. Worth checking out.